Superflare of a Sun-like star observed with XMM-Newton and SRG/eROSITA

In this work, we studied X-ray source SRGe J021932.4$-$040154 (SRGe J02193), which we associated with a single X-ray active star of spectral class G2V$-$G4V and the rotational period Pᵣₒₜ < 9.3 days. Additional analysis of TESS light-curves allowed for the rotational period estimation of 3.2 ± 0.5 days. SRGe J02193 was observed with the SRG/eROSITA during eUDS survey in 2019 in a much dimmer state compared to the XMM-Newton catalogue 4XMM-DR12. Detailed analysis revealed that the archival XMM-Newton observations captured the source during a flaring event in 2017. The XMM-Newton light curve demonstrates a strong flare described with the Gaussian rise and exponential decay, typical for stellar flares, characterized by timescales of ~400 s and ~1300 s, respectively. The spectral analysis of the quiescent state reveals ~10 MK plasma at luminosity of (1.4±0.4) × 10²⁹ ~erg~s⁻¹ (0.3$-$4.5 keV). The spectrum of the flare is characterized by temperature of ~40 MK and luminosity (5.5±0.6)× 10³⁰ ~erg~s⁻¹. The total energy emitted during the flare ~1.7 × 10³⁴ erg exceeds the canonical threshold of 10³³ erg, allowing us to classify the observed event as a superflare on a Sun-like star. Additionally, we present the upper limit on the surface starspot area based on the brightness variations and consider the hypothesis of the object being a binary system with G-type and M-type stars, suggested by two independent estimations of radial velocity variations from APOGEE-2 and Gaia.